A facile and mild reduction procedure is reported for the preparation of chiral secondary alcohols prepared from α-substituted ketones using sodium borohydride and the chiral boronate ester (l)-TarB-NO2. Direct reduction of substituted ketones bearing Lewis basic heteroatoms generally provided secondary alcohols of only modest enantiomeric excess likely due to either competition between the target
for exceptional catalytic turnover numbers (up to 15 400), which were increased by around 1.5–3 orders of magnitude compared to the most active catalysts previously reported. In our concept an aprotic ammonium halide moiety cooperates with an oxophilic Lewisacid within the same catalyst molecule. Control experiments reveal that both catalytic centers are essential for the observed activity. Kinetic
Asymmetric Grignard Synthesis of Tertiary Alcohols through Rational Ligand Design
作者:Bartosz Bieszczad、Declan G. Gilheany
DOI:10.1002/anie.201610462
日期:2017.4.3
enantioselective construction of tertiaryalcoholsthrough the direct addition of organomagnesium reagents to ketones. Discovered by rational ligand design based on a mechanistic hypothesis, it has an unprecedented broad scope. It utilizes a new type of chiral tridentate diamine/phenol ligand that is easily removed from the reaction mixture. It is exemplified by application to a formal asymmetric synthesis
Chiral Chromium Salen@rGO as Multipurpose and Recyclable Heterogeneous Catalyst
作者:Mariam Abd El Sater、Mohamed Mellah、Diana Dragoe、Emilie Kolodziej、Nada Jaber、Emmanuelle Schulz
DOI:10.1002/chem.202101003
日期:2021.6.25
to promote asymmetric catalysis in repeated cycles, without loss of activity or enantioselectivity. This specific behavior was demonstrated in two different catalytic reactions (up to ten reuses) promoted by chromium salen complexes, the cyclohexene oxide ring-opening reaction and the hetero-Diels-Alder cycloaddition between various aldehydes and Danishefsky's diene. Furthermore, the chiral chromium
An Aluminum Fluoride Complex with an Appended Ammonium Salt as an Exceptionally Active Cooperative Catalyst for the Asymmetric Carboxycyanation of Aldehydes
Al−F bonds are among the most stable σ bonds known, exhibiting an even higher bond energy than Si−F bonds. Despite a stability advantage and a potentially high Lewis acidity of Al−F complexes, they have not been described as structurally defined catalysts for enantioselective reactions. We show that Al−F salen complexes with appended ammonium moieties give exceptional catalytic activity in asymmetric